This invention relates to improvements in the guidewires, particularly guidewires used in small bore blood vessels such as those involved in angioplasty procedures. U.S. Pat. No. 4,545,390 to Leary discloses a small diameter (no greater than about 0.020" in diameter) steerable guidewire which can be advanced and steered into and along very narrow blood vessels to locate the distal end of the guidewire in a precise position in a selected blood vessel branch. Once the guidewire has been so placed, a catheter can be advanced over the guidewire directly to the desired location in the patient's cardiovascular system to enable the catheter to perform its intended function at that location. For example, the invention is particularly useful in coronary angioplasty procedures in which a small diameter balloon dilatation catheter is placed in a narrowed region of a coronary artery so that the balloon may be inflated to widen the lumen of the artery.
U.S. Pat. No. 4,545,390 to Leary discloses a small diameter steerable guidewire which is capable of transmitting from its proximal end to its distal end substantially all of the angular rotation applied to the proximal end. The distal end of the guidewire is adapted to be bent to a set curve by the surgeon before the guidewire is placed in the patient. After the guidewire has been placed in the patient's blood vessel, it may be steered to select between branches of the patient's cardiovascular system by rotating the proximal end of the guidewire to direct selectively the bent distal end of the guidewire to the desired branch. Typically, the guidewire is advanced through the blood vessels while being monitored fluoroscopically.
The steerable guidewire described in the Leary patent was the first small diameter guidewire that could be steered effectively and enabled balloon dilatation procedure to be performed in small diameter distal blood vessels which previously had been unreachable. However, the curve which the surgeon forms at the distal tip of the guidewire, before inserting it into the patient, necessarily involves an approximation by the surgeon as to the degree of curvature best suited for the particular procedure to be performed. Sometimes, after the guidewire has been placed, the degree of bend placed in the distal tip proves to be too great or too little to enable the tip to be steered into a selected blood vessel. Under those circumstances, the physician may have to withdraw the guidewire, reform the bend at its distal tip and then reinsert the guidewire. That complicates and delays the procedure undesirably. It is among the principal objects of the present invention to provide a small diameter steerable guidewire in which the degree of curvature at the distal tip of the guidewire may be adjusted and controlled while the guidewire remains placed in the patient and without requiring removal and manual reshaping of the guidewire.